lift needle piston, symptoms for which carb?

[deadflo]

Hey I got a carb synch tool and worked on balancing my carbs on my 71 this weekend. I think I did ok, the car is running pretty good , although it wasn't that far off, but i have a question about setting the carb mixtures.

When I lifted a piston in one carb to check the mixture, the engine continued to run ..roughly, so i'm told that means my mixture is a bit rich.

OK, so when i went to raise the piston in the other carb she started to die, so that means Im running a bit lean.

Does this mean when i raise a piston in one carb, the engine symptoms point to the condition of that carb, or the one I'm not raising the piston in??

This may sound like a dumb question, but some info indicates when you raise the piston, youre making that carb inoperable,so I'm not sure if the symptons shown are for a carb that isnt working, or the one that is...

[240ZX]

Steve,

If I may suggest...........purchase the video from Ztherapy. It will answer your question as well as other questions regarding the SU carbs.

[deadflo]

Hey , you know I actually have purchased the video! I tried to wade through it again to find any reference to the piston lifting trick and couldn,t find it. I did find one shot of the piston being lifted but no dialouge to mention what he was looking for. I have seen the reference to lifting the piston on three different websites, but no one was real clear about which carb the process was indicating the mixture for.

Also, one website says to lift the needle pistion 1/8 of an inch, another to lift it nearly to the top...so im still a bit confused.

[240ZX]

Well,

Let's think about it.........what happens when you lift one of the needle/slide assys? Isn't lifting the needle/slide essentially the same as leaning the mixture for that particular carb (a whole lot more air than fuel)? So thats probably why, if it's a bit too rich, it will continue to run and if it's a bit too lean it will start to stumble and die. So it most likely indicates the mixture of the carb you are lifting the needle/slide on. Does this uncloud the picture a bit better? I hope so!

[beandip]

If you go to the tec section there is a step by step walk through on how to do this. When you lift the piston, this does disable the carb and the engine is running on the other one, if the engine dies that carb is too lean , if it stumbles but continues to run its ok. If on the other hand continues to run smoothly it is too rich. Adjust it accordingly and repeat the whole thing on the secound one. So you lift the piston on the rear carb and adjust the front one . Then lift the front piston and adjust the rear one .Read the teck "how to " and it covers lean pop as well. Gary:classic: